From: Robert Klemme <shortcutter@...>
Date: 2010-12-19T00:50:23+09:00
Subject: Re: background threads

On 18.12.2010 15:10, Venkat Akkineni wrote:
> Mike
>
>
>          Thanks for your reply. The flag is wrong indeed. I didn't notice
> this because the 'else' part of setSignal never gets executed with the
> current setup. You will notice that the program runs exactly the same
> way even when all commands inside setSignal except call to
> display function are commented.
>
> def setSignal(signal)
> #    if signal == true
>        display
> #    else
> #      self.aFlag=true
> #    end
>    end
>
> When I change the display function to the following
>
>   def display
>      self.run
>      sleep 20
>    end
>
> program prints 'I am here' after 20 seconds.
>
> The reason I did not have an argument for sleep is I wan't the thread
> run indefinitely until I call it off some how. This is the desired
> effect.
>
> Two approaches I have tried are
>
> 1.) loop through indefinitely around necessary code block.

I am not sure what you mean.

> 2.) create a thread around the above loop and call Thread.join.

If you create a thread and then do nothing but joining it you don't need 
a thread at all.

> Both the above approaches stop execution where ever these blocks are
> called from. Hence I am unable to push the execution of the thread to
> the background.
>
> Your thoughts and help ...

I have no idea how your code looks and what exactly you are describing 
here.  This is what I'd do.

require 'monitor'

class Example
   include MonitorMixin

   def keep_running=(x)
     synchronize do
       @keep_running = x
     end
   end

   def keep_running?
     synchronize do
       @keep_running
     end
   end

   attr_reader :thread

   def display
     self.keep_running = true

     @thread = Thread.new do
       i = 0

       while keep_running?
         printf "%-20s %5d\n", "Background", i
         i += 1

         sleep 1
       end
     end
   end
end

e = Example.new
e.display

10.times do |i|
   printf "%-20s %5d\n", "Foreground", i
   sleep 3
end

e.keep_running = false

e.thread.join

puts "done."

Kind regards

	robert



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